In order to improve process uniformity in a surface of a processing target object such as a semiconductor wafer, there has been proposed a method of changing a supply amount of a processing gas at a central portion and an edge portion of the wafer (see, for example, Patent Document 1).
In Patent Document 1, in order to change the supply amount of the processing gas at the central portion and the edge portion of the wafer, a circular ring-shaped partition wall is provided in a buffer room (gas diffusion space) of an upper electrode configured to discharge the processing gas. The buffer room is partitioned into a central buffer room and an outer buffer room, and the processing gas is supplied into the respective buffer rooms at different supply amounts.    Patent Document 1: Japanese Patent Laid-open Publication No. 2006-165399
In Patent Document 1, the circular ring-shaped partition wall is placed at a position capable of obtaining highest process uniformity in the surface of the wafer.
Since, however, the position of the circular ring-shaped partition wall is fixed, if there is a change in the process, e.g., a change in processing conditions, a margin for obtaining desired uniformity in the surface of the wafer would be reduced or best uniformity in the surface of the wafer may not be obtained. In such a case, a discharging position of the processing gas discharged to the central portion in the surface of the wafer and a discharging position of the processing gas discharged to the edge portion in the surface of the wafer need to be changed each time. For example, in Patent Document 1, the position of the circular ring-shaped partition wall needs to be changed or the circular ring-shaped partition wall needs to be replaced manually. Alternatively, the upper electrode itself, i.e., a processing gas discharge unit itself needs to be replaced manually.
The same problems as mentioned above may also occur when a new process is employed in order to manufacture a next-generation device as well as when there is a change in the process. For this reason, a conventional processing apparatus has low compatibility with or applicability to a next-generation device or process.